The purpose of this study is to elucidate the mechanical factors that lead to restoration of a cartilaginous articular surface, decreased pain, and improved joint function after mechanical distraction of osteoarthritic joints. We propose a randomized controlled trial of distraction with and without motion as treatment for ankle osteoarthritis, and to simultaneously collecting imaging and biological data that we can use to improve our understanding of the pertinent biophysical factors influencing patient outcomes. We will explore several related hypotheses, including 1) Ankle motion during distraction will result in clinically significant improvements in patient-derived outcome measures and increased cartilage thickness distribution over the most heavily loaded portion of the articular surface, as compared to the use of distraction without ankle motion; 2a) Ankles with low geometric surface irregularity and greater range of motion will have better preservation of neo-chondroid tissue (increased normalized cartilage thickness and reduced longitudinal compressive strain distribution over the habitually heavily loaded regions of the articular surface) than those with high surface irregularity; 2b) Ankles with low geometric surface irregularity and greater range of motion have reduced habitual focal or regional contact stress elevation; and 3) Joints that have better improvements in patient derived outcome measures and improved cartilage thickness distribution over habitually heavily loaded portion of the articular surface will have improved normalization of synovial fluid markers of biosynthetic and oxidative activity. The studies we propose involve a multi-disciplinary approach utilizing both laboratory and clinical research to focus on improving our understanding of the pathomechanics and treatment of osteoarthritis. We will bring state-of-the-art techniques for clinical assessment, articular surface imaging, biomechanical modeling, and biochemical testing within the framework of a mutually supportive interaction between basic scientists and clinical investigators. New knowledge of the biophysical determinants of articular repair in OA will lead to improved treatment and reduce the substantial associated morbidity and suffering from OA.